Invariably for some fraction of transactions you'll later find out the settlement shouldn't have been executed. It doesn't matter whose "fault" that is, either way somebody will get screwed when this happens. If you wait longer, you may detect this before settlement completes and nobody gets screwed.
In my country there's a scam where people find out you're buying a house through a particular solicitor with a large cash transfer, then they send you an email or even a physical letter saying there's a problem, the solicitor just found out their firm got a new bank, or whatever, please transfer the house money to the new account. Of course it's a lot of money so most people will want to check this is right - they provide their phone number on the message. This number, of course, is part of the scam and a "secretary" will answer saying your solicitor is busy right now, but yes, they're very sorry, the message is genuine and please use the new account details.
The large sums involved mean this scam is very lucrative even if it doesn't work on say, 99% of potential victims.
If the victim realises they've been scammed ten minutes after the transfer, chances are good the bank can fix it, because settlements aren't really instant. If they realise the next day, or two, or three days later, the money is gone. It went to a mule, who has already forwarded it, the police might arrest the mule if they can find them, but the mule doesn't have your money, they're just another sucker.